I noticed that this much-loved sign had been covered over a few months ago. According to today's Liverpool Echo the sign was removed and new adverts put in its place as part of the cleanup for 2008.
The 'Look Of The City' project targeted 10 sites to make the city more 'presentable'. Also included in the project is the removal of the Las Vegas sign from the property by Lime Street.
Update (6 July 2007): Las Vegas improvement - the £1 larger bar